During the life cycle of a hydrocarbon well, e.g., a well for extracting oil or natural gas from the Earth, the producing well commonly also yields water. In these instances, the amount of water produced from the well tends to increase over time with a concomitant reduction of hydrocarbon production. Frequently, the production of water becomes so profuse that remedial measures have to be taken to decrease the water/hydrocarbon production ratio. As a final consequence of the increasing water production, the well has to be abandoned.
Various techniques have been developed and used for reducing the quantity of water produced from oil and/or gas wells. Under normal circumstances, an open production interval is formed so that the well communicates with the hydrocarbon-bearing zone(s) of the formation but does not extent into and communicate with the water-bearing portion(s). However, the open production interval formed may inadvertently communicate with a water-bearing zone which is completed in the same wellbore.
Even if there is no actual initial fluid communication between the open production interval and the water-bearing zones of the formation, such communication may develop during production of hydrocarbon. For example, water may be drawn upwardly from the water-bearing portion in a process known as water coning.
To counteract the effects of water-influx and/or coning, U.S. Pat. No. 3,719,228 discloses for example a method of treating a subterranean formation containing hydrocarbons and brine to stimulate the production of hydrocarbons: A preflush composition comprised of a water solution of rosin soap and fatty acid soap is injected into the formation. The preflush reacts with connate brine to produce a precipitate that blocks the brine-bearing passages. The composition does not react with hydrocarbons thereby allowing hydrocarbon-bearing passages to remain open.
Another alternative method is disclosed in U.S. Pat. No. 4,617,132: A sandstone formation is contacted with an aqueous solution containing a water soluble anionic polymer having a molecular weight greater than 100,000. As the next step, the anionic polymer is contacted with a fluid containing a water soluble cationic polymer having a weight greater than 1,000. As a result of the contact of the anionic with the cationic polymer, coacervation occurs between the two polymers which reduces the amount of the anionic polymer removed from the formation by fluids produced therefrom. The presence of stabilized polymer in the formation reduces the water/oil ratio by reducing the permeability of the formation to water in the wellbore area.
U.S. Pat. No. 5,146,986 discloses another method of selectively reducing the permeability of a subterranean formation. The formation is contacted with a hydrocarbon carrier liquid containing a surface active agent. The surface active agent is believed to adsorb on the walls of the interstitial passages in the formation as a result of which, the flow of water through the passages is reduced.
U.S. Pat. No. 5,150,754 discloses a method of, firstly, selectively injecting into a hydrocarbon-bearing zone a petroleum mixture capable of forming a solid gel that degrades over a designated period of time. In a second step, an aqueous gel-forming mixture is injected into a water influx zone of the formation. Upon degradation of the first gel, production of hydrocarbons can continue.
Another method, disclosed in U.S. Pat. No. 5,203,834, comprises the steps of injecting a gas, a polymer composition capable to form a foamed gel with the gas, and a delayed gel degrading agent being capable of opening pathways in the gel.
Furthermore, K. E. Thomson and H. S. Fogler published in SPE Production and Facilities, May 1995, pp. 130-137, a proposal using an injection backflow and shut-in procedure, using a slow reacting silica based diverting agent. The backflow step is described as a miscible displacement of the agent before the onset or completion of the gelation.
The object of this present invention is to provide improved methods for water control.